Salmon and Salmonidae. 1 The Salmonidae are an important family of fishes belonging to the Malacopterygian Teleosteans, characterized as follows: Margin of the upper jaw formed by the premaxillaries and the maxillaries - supraoccipital in contact with the frontals, but frequently overlapped by the parietals, which may meet in a sagittal suture; opercular bones all well developed. Ribs sessile, parapophyses very short or absent; epineurals, sometimes also epipleurals, present. Post-temporal forked, the upper branch attached to the epiotic, the lower to the opisthotic; postclavicle, as usual, applied to the inner side'of the clavicle. A small adipose dorsal fin. Air-bladder usually present, large. Oviducts rudimentary or absent, the ova falling into the cavity of the abdomen before extrusion.
The Salmonidae are very closely related to the Clupeidae, or herring family, from which they are principally distinguished by the position of the postclavicle and by the presence of a rayless fin on the back, at a considerable distance from the true or rayed dorsal fin; this so-called adipose fin is an easy recognition-mark of this family, so far as British waters are concerned, for, if it is present in several other families, these have no representatives in the area occupied by the fresh-water salmonids, with the exception of the North American Siluridae and Percopsidae, which are readily distinguished by the pungent spine or spines which precede the rays of the first dorsal fin. The imperfect condition of the oviducts, quite exceptional among fishes, owing to which the large ripe eggs may be easily squeezed out of the abdomen, is a feature of great practical importance, since it renders artificial impregnation particularly easy, and to it is due the fact that the species of Salmo have always occupied the first place in the annals of fish-culture.
The Salmonidae inhabit mostly the temperate and arctic zones of the northern hemisphere, and this is the case with all freshwater forms, with one exception, Retropinna, a smelt-like fish from the coasts and rivers of New Zealand. A few deep-sea forms (Argentina, Microstoma, Nansenia, Bathylagus) are known from the Arctic ocean, the Mediterranean and the Antarctic ocean, down to 2000 fathoms. The question has been discussed whether the salmonids, so many of which live in the sea, but resort to rivers for breeding purposes, were originally marine or fresh-water. The balance of opinion is in favour of the former hypothesis, which is supported by the fact that the overwhelming majority of the members of the suborder of which the salmonids form part permanently inhabit the sea. The clupeids, 1 The Latin name salmo possibly means literally "the leaper," from salire, to leap, jump.
for instance, which are their nearest allies, are certainly of marine origin, as proved by their abundance in Cretaceous seas, yet a few, like the shads, ascend rivers to spawn, in the same way as the salmon does, without this ever having been adduced as evidence in favour of a fresh-water origin of the genus Clupea to which they belong.
No remains older than Miocene (Osmerus, Prothymallus, Thaumaturus) are certainly referable to this family, the various Cretaceous forms originally referred to it, such as Osmeroides and Pachyrhizodus, being now placed with the Elopidae. There is probably no other group of fishes to which so much attention has been paid as to the Salmonidae, and the species have been unduly multiplied by some writers. Perhaps not more than 80 should be regarded as valid, but some of them fall into a number of local forms which are distinguished as varieties or subspecies by some authors, whilst others would assign them full specific rank. These differences of opinion prevail whether we deal with Salmo proper or with Coregonus. Classification. - The recent genera may be arranged in five groups: The first, which includes Salmo, Brachymystax, Stenodus, Coregonus, Phylogephyra and Thymallus, has 8 to zo branchiostegal rays, 9 to 13 rays in the ventral fin, the pyloric appendages more or less numerous (17 to 200) and breeding takes place in fresh water. The second group, with the single genus Argentina, is, like the following, marine, and is characterized by 6 branchiostegal rays, i i to 14 ventral rays, the stomach caecal, with pyloric appendages in moderate numbers (12 to 20). The third group, genera Osmerus, Thaleichthys, Mallotus, Plecoglossus, Hypomesus, has 6 to 10 branchiostegal rays, 6 to 8 ventral rays, the stomach caecal, with pyloric appendages few (2 to 11) or rather numerous. The fourth group, genera Microstoma, Nansenia, Bathylagus, deep-sea forms with the branchiostegal rays reduced to 3 or 4, ventral rays 8 to 10, the stomach caecal and pyloric appendages absent; whilst the fifth group, with the genera Retropinna and Salanx, is distinguished from the preceding in having no air-bladder, branchiostegal rays 3 to 6, ventral rays 6 or 7, stomach siphonal and pyloric appendages absent.
The genus Salmo, the most important from the economical and sporting points of view, is characterized by small smooth scales, which at certain seasons may become embedded in the slimy skin, a moderately high dorsal fin with 10 to 12 well-developed rays, and a large mouth provided with strong teeth, which are present not only in the jaws and on the palate, but also on the tongue; the maxillary or posterior bone of the upper jaw extends to below or beyond the eye. Young specimens (see Parr) are marked with dark vertical bars on the sides (parr-marks), which in some trout are retained throughout life, and have the caudal fin more or less deeply forked or marginate, the form of the fin changing with the age and sexual development of the fish. Adult males have the jaws more produced in front than females, and both snout and chin may become curved and hooked. As pointed out by A. Gunther, who was the first to make a profound study of the members of this genus, and especially of the British forms, there is probably no other group of fishes which offers so many difficulties to the ichthyologist with regard to the distinction of species, as well as to certain points in their life-history, the almost infinite variations which they undergo being dependent on age, sex and sexual development, food and the properties of the water. The difficulties in their study have rather been increased by the excessive multiplication of so-called specific forms. Opinions also vary as to the importance to be attached to the characters which serve to group the principal species into natural divisions. Whilst A. Gunther admitted two genera, Salmo and Oncorhynchus, D. S. Jordan and B. W. Evermann go so far as to recognize five, Oncorhynchus, Salmo, Hucho, Cristivomer and Salvelinus. The latter arrangement is certainly the more logical, the difference between the first genus and the second being of rather less importance than that between the second and the third. However, considering the slightness of the distinctive characters on which these divisions are based, and the complete passage which obtains between them, the writer of this article thinks it best to maintain the genus Salmo in the wide sense, whilst retaining the divisions as subordinate divisions or sub-genera, with the following definitions Oncorhynchus (Pacific salmon). - Vomer flat, toothed along the shaft, at least in the young; anal fin with 12 to 17 well-developed rays.
Salmo (true salmon and trout). - Vomer flat, toothed along the shaft, at least in the young; anal fin with 8 to 12 well-developed rays. Salvelinus (char). - Vomer boat-shaped, the shaft strongly depressed behind the head, which alone is toothed, the teeth forming an isolated fascicle; anal fin with 8 to to well-developed rays.
Hucho (huchens). - Vomer as in the preceding, but teeth forming a single arched transverse series continuous with the palatine teeth; anal fin with 8 to 10 well-developed rays.
The salmon itself (Salmo salar), the type of the family, is a large fish, attaining a length of 4 or 5 ft., and living partly in the sea, partly in fresh water, breeding in the latter. Fish which thus ascend rivers to spawn are called "anadromous." It may be briefly defined as of silvery coloration, with small black spots usually confined to the side above the lateral line, with the teeth on the shaft of the vomer disappearing in the adult, with 18 to 22 gill-rakers on the first branchial arch, with I i or 12 welldeveloped rays in the dorsal fin, i i o to 125 scales in the lateral line, and z i or 12 (exceptionally 13) between the latter and the posterior border of the adipose fin. The young, called "parr" or "samlet," characterized by a smaller mouth, the maxillary bone not extending much beyond the vertical of the centre of the eye, the presence of an alternating double or zigzag series of teeth on the shaft of the vomer, the presence of dark vertical bars on the sides of the body, together with more or less numerous small red spots, is hatched in the spring, and usually remains for about two years in the rivers, descending at the third spring to the sea, where it is known as "smolt." In the sea it soon assumes a more uniform silvery coloration and from this state, or "grilse," develops its sexual organs and re-enters rivers to breed, after which operation, much emaciated and unwholesome as food, it is known as "kelt," and returns to the sea to recuperate. It has now been ascertained by the investigations instituted in Norway by K. Dahl that the smolts, immediately after leaving the rivers, make for the open sea, and do not return to the coast until they have reached the grilse stage. Thus specimens measuring between 8 and 18 in. hardly ever fall into the hands of the angler.
The salmon inhabits the North Atlantic and its tributary waters. It is known to extend as far north as Scandinavia, Lapland, Iceland, Greenland and Labrador, and as far south as the north-west of Spain and the state of Connecticut. It ascends the Rhine as far as Basel. There are land-locked forms in Scandinavia and in Canada and Maine, which are regarded by some authors as distinct species (S. hardinii from Lake Wener, S. sebago from Sebago Lake in Maine, S. ouananiche from Lake St John, Canada and neighbouring waters). These nonmigratory forms are smaller than the typical salmon, never exceeding a weight of 25 lb, the ouananiche, the smallest of all, rarely weighing 7 2lb and averaging 3. Although spending their whole life in fresh waters, the habits of these fish are very similar to those of the sea salmon, ascending tributary streams to spawn in their higher ranges, and then returning to the deep parts of the lakes, which are to them what the sea is to the anadromous salmonids.
The salmon breeds in the shallow running waters of the upper streams of the rivers it ascends. The female, when about to deposit her eggs, scoops out a trough in the gravel of the bed of. the stream. This she effects by lying on her side and ploughing into the gravel by energetic motions of her body. She then deposits her eggs in the trough; while she is engaged in these operations she is attended by a male, who sheds milt over the eggs as the female extrudes them, fertilization being, as in the great majority of Teleostei, external. The parent fish then fill up the trough and heap up the gravel over the eggs until these are covered to a depth of some feet. The gravel heap thus formed is called a "redd." The period of the year at which spawning takes place in the British Isles, and in similar latitudes of the northern hemisphere, varies to a certain extent with the locality, and in a given locality may vary in different years; but, with rare exceptions, spawning is confined to the period between the beginning of September and the middle of January.
The eggs are spherical and non-adhesive; they are heavier than water, and are moderately tough and elastic. The size varies slightly with the age of the parent fish, those from full-sized females being slightly larger than those from very young fish. According to rough calculations made at salmon-breeding establishments, there are 25,000 eggs to a gallon; the diameter is about a quarter of an inch. It is usually estimated that a female salmon produces about 900 eggs for each pound of her own weight; but this average is often exceeded.
The time between fertilization and hatching, or the escape of the young fish from the egg-membrane, varies considerably with the temperature to which the eggs are exposed. It has been found that at a constant temperature of 41° F. the period is 97 days; but the period may be as short as 7 0 days and as long as 150 days without injury to the health of the embryo. It follows therefore that in the natural conditions eggs deposited in the autumn are hatched in the early spring. The newly hatched fish, or "alevin," is provided with a very large yolk-sac, and by the absorption of the yolk is nourished for some time; although its mouth is fully formed and open, it takes no food. The alevin stage lasts for about six weeks, and at the end of it the young fish is about it in. long.
The grilse, after spawning in autumn, return again to the sea in the winter or following spring, and reascend the rivers as mature spawning salmon in the following year. Both salmon and grilse after spawning are called "kelts." The following recorded experiment illustrates the growth of grilse into salmon: a grilse-kelt of 2 lb was marked on March 31, 1858, and recaptured on August 2 of the same year as a salmon of 81b.
The ascent of rivers by adult salmon is not so regular as that of grilse, and the knowledge of the subject is not complete. Although salmon scarcely ever spawn before the month of September, they do not ascend in shoals just before that season; the time of ascent extends throughout the spring and summer. A salmon newly arrived in fresh water from the sea is called a clean salmon, on account of its bright, well-fed appearance; during their stay in the rivers the fish lose the brilliancy of their scales and deteriorate in condition. The time of year at which clean salmon ascend from the sea varies greatly in different rivers; and rivers are, in relation to this subject, usually denominated early or late. The Scottish rivers flowing into the German Ocean and Pentland Firth are almost all early, while those of the Atlantic slope are late. The Thurso in Caithness and the Naver in Sutherlandshire contain fresh-run salmon in December and January; the same is the case with the Tay. In Yorkshire salmon commence their ascent in July, August or September if the season is wet, but if it is dry their migration is delayed till the autumn rains set in. In all rivers more salmon ascend immediately after a spate or flood than when the river is low, and more with the flood tide than during the ebb. In their ascent salmon are able to pass obstructions, such as waterfalls and weirs of considerable height, and the leaps they make in surmounting such impediments and the persistence of their efforts are very remarkable.
Herring . Crustacea, amphipods, &c. Sand eels . Haddock and whiting . Feathers and vegetable matter . |
. |
36 or 4 7 14 „ 18 0 1 1 „ 1 4% o? 8 „ 10 i° 7 „ 9% |
We reproduce here, with additions, Professor Noel Paton's summary (published first in the moth edition of this Encyclopedia) of observations on the life-history of the salmon. Important advances in our knowledge of the life-history of the salmon have been made through the investigations of Professor F. Miescher on the Rhine at Basel, of Professor P. P. C. Hoek in Holland, of Mr Archer as lessee of the river Sands in Norway and as inspector of salmon fisheries for Scotland in conjunction with Messrs Gray and Tosh, and of a number of workers in the laboratory of the Royal College of Physicians of Edinburgh. With regard to the food of salmon, the enormously rapid growth of smolts to grilse and of salmon from year to year shows that they feed in the sea. In a few months a smolt will increase from a few ounces to 4 or 5 1b; while Archer's weighings of 16 salmon which had been marked and recaptured in the following year 'showed an average gain of 36%, reckoned on from kelt stage to kelt stage. During the season of 1895 Tosh, at Berwick-on-Tweed, opened between March and August 514 fish, and found food in the stomachs of 76, or over 14% of the whole. As to the nature of the food, it was found to be as follows: Excluding the feathers and vegetable matter, which are not really of the nature of food, all the material found in the stomach was of marine origin. Hoek, out of 2000 fish examined by him, found 7 with food in the stomach, and, curiously enough, 4 of these were taken on the same day. In each case marine fish constituted the food. As to where salmon go to feed in the sea, our information is still very deficient, but the prevalence of herring in the stomach would seem to indicate that they must follow the shoals of these fish which approach the coast during the summer months. While there can be no doubt that salmon feed in the sea, the question of whether they feed in fresh water has been much debated. It is difficult for the popular mind to conceive of an active fish like the salmon subsisting for several months without food, and the fact that the fish so frequently not only takes into its mouth but actually swallows worms and various lures has still further tended to confirm many people in the conviction that salmon do feed in fresh water. In discussing the question it is well clearly to understand what is meant by feeding. It is the taking, digesting and absorbing of material of use in the economy in such quantities as to be of benefit to the individual. Accepting this definition, it may at once be said that all the evidence we possess is entirely opposed to the view that salmon feed when in fresh water. Miescher examined the stomachs of about 2000 salmon captured at Basel, about 500 m. from the mouth of the Rhine, and in only two did he find any indication of feeding. These two fish were male kelts. One contained the remains of a cyprinoid fish, and the other had a dilated stomach with an acid secretion, but no food remains. Hoek, who, as already stated, examined about 2000 fish, found food of marine origin in 7, but in none food derived from fresh water. Of the 132 stomachs of salmon from the estuaries and upper waters of Scottish rivers examined in the laboratory of the College of Physicians not one contained any food remains. The stomach of salmon captured in fresh water is collapsed and shrunken. Its mucous membrane is thrown into folds, and it contains a small amount of mucus of a neutral reaction. The intestine, which usually contains numerous tape-worms, is full of a greenish-yellow viscous material which, when examined under the microscope, is found to consist of mucus with shed epithelial and other cells and with masses of crystals of carbonate of lime. In no case does the microscope reveal any food remains such as fish-scales, plates of crustacea or bristles of worms or annelids. In the fish taken in the estuaries up to the month of August the gall-bladder is distended; in those taken later in the year it is empty. In all the fish from the upper waters the gall-bladder is empty and collapsed. According to the investigations of Hoek and of Gulland, the lining membrane of the stomach and intestine degenerates while the fish is in the river, but the correctness of these observations has been denied by F. B. Brown and J. Kingston Barton. Gillespie finds that the activity of the digestive processes is low in fish taken from the rivers, and that micro-organisms, which would be killed by the hydrochloric acid of the gastric juice were it actively secreted, flourish in he intestines of the fish from the upper waters. Those who believe that the salmon feeds in fresh water explain the fact that the stomach is always found empty by the supposition that the fish vomits any food when it is captured, and several descriptions of cases in which this has been observed might be quoted; but such observations must be accepted with caution, and the contracted state of the stomach, the absence of the hydrochloric acid of the gastric juice, and lastly the absence of any traces of digested food remains in the contents of the intestine, negative this explanation.
The question may be presented in another way. Is there any reason why the salmon should feed while in fresh water? The investigations carried on in the laboratory of the College of Physicians have definitely shown that the salmon leaves the sea with an enormous supply of nourishment stored in its muscles, and that during its sojourn in fresh water it gets its energy and builds up its rapidly growing ovaries and testes from this stored material. Briefly stated, these investigations show that the supply of albuminous material and fats stored in the muscles and used while the fish is in the river is amply sufficient for the greatest requirements of the fish. The amount of energy liberated from the fats and albuminous material is 570 times more than is required to raise the fish from the level of the estuary to that of the upper waters! These analyses further show that all the materials required for the construction of the ovaries and the testes are found in sufficient quantity in the muscles, with the exception of iron, which is, however, abundantly present in the blood.
It is a very common opinion that kelts feed voraciously while still in fresh water, and this has been used as an argument that they should be destroyed. It is not easy to bring forward such satisfactory evidence as has been adduced in the case of unspawned salmon, since it is illegal to kill kelts; but none of,' the 25 kelts procured by the Scottish Fishery Board, and examined in the College of Physicians' laboratory, contained any food, and Mr Anderson, formerly of Dunkeld, informs Professor Paton that in the old days, when kelts were habitually killed when captured, he has opened a large number and never found any trace of food in the stomach. Some fishers declare that they have seen kelts devouring salmon fry, but it is not easy to make accurate observations in deep water. According to Dr Gulland's investigations, the mucous membrane of the stomach and intestine is completely regenerated while the gall-bladder contains bile, and the digestive activity of the alimentary canal is greater than in salmon before spawning. Kelts thus appear at least to be capable of feeding.
The rate of growth of the genitalia has been carefully studied by Miescher, Archer and Hoek. From January till about the end of May the growth of the ovaries is slow. In Hoek's series of observations, which are the most complete, they increased from 35 to 85% of the body weight. After this they enlarge more rapidly, and by the end of August are about 3% in salmon taken at the mouth of the Tweed, about 4% in the salmon from the mouth of the Rhine and about 8% in the salmon from the Basel fisheries. By November they have risen to 20% in the Tweed and in Holland, and to 23% in the upper reaches of the Rhine. According to Archer's observations, the development of the ovaries in grilse in the earlier months somewhat lags behind that in the salmon. The growth of the testes has been chiefly investigated by Archer and Tosh in the Tweed and by Miescher at Basel. From March to the middle of July in the Tweed these organs increase from about .19 to 35% of the weight of the fish. In July their rate of growth increases, and they reach their maximum development at the end of September, when they are about 6% of the body weight. In the Rhine in March they weigh about. 1%, and they reach their maximum development of about 5% in October.
May |
July |
Oct. |
||||||
Nov. 1 |
Feb. |
Mar. |
April. |
and |
and |
and |
Kelts. |
|
June. |
Aug. |
Nov. |
||||||
Muscles |
2481 |
2214 |
2 355 |
2 599 |
2210 |
2270 |
1 75 o |
946 |
Ovaries |
23 |
24 |
24 |
33 |
47 |
72 |
545 |
9 |
Total |
2504 |
2238 |
2379 |
2632 |
22 57 |
2 34 2 |
22 95 |
955 |
What leads to the migration of salmon from sea to river and river to sea? It is usually supposed that they come to the river to spawn; that it is the nisus generativus that drives them from the sea, where their ova will not develop, to the fresh water where development is possible. But it is found that salmon are passing from sea to river at all seasons of the year, and with their genitalia in all stages of development - some fish, running in March with ovaries only I % of the body weight, other fish not running till October with ovaries 15 or 16% of the body weight. It is difficult, then, to accept the theory that the sexual act is the governing factor. That it is a secondary factor seems to be indicated by the great run of fish in June, July and August, when the genitalia are most rapidly growing. There is one respect, however, in which all the fish leaving the sea for the river agree, and that is in the amount of stored material accumulated in their bodies. In the early running fish this material is largely confined to the muscles, but in the later coming fish it is more equally distributed between muscles and genitalia. The amount of stored material may be measured by the amount of solids, and if we express the results of all the fish examined in terms of fish of uniform size - loo cm. in length - the following results are obtained: - It would thus appear that, when the salmon has in the sea accumulated a certain definite amount of nourishment, it ceases to feed, and returns to the river irrespective of the state of its genital organs. Nutrition, and not the nisus generativus, appears to be the motive power. That the fish after spawning returns to the sea in search of food is fully recognized by all.
Course of Migration
It is well known that while salmon run all the year through in greater or lesser numbers, the run of grilse takes place in the summer months, from May to August. But it is further possible to divide the salmon into classes - the so-called winter salmon of the Rhine, large fish running from October to February, with unripe ovaries and testes; and the summer salmon, running for the most part from March to October, with genitalia more or less ripe. These summer fish are small in the early months, but increase in size as the autumn advances. The winter salmon, along with the early summer or spring fish, appear to pass directly to the upper reaches of the river, and to spawn there, while the larger late-coming fish appear to populate the lower waters. This seems to be indicated by the comparison of upper-water and estuary fish throughout the year. The period at which male and female fish enter the rivers also appears to be somewhat different. The observations of Tosh, Miescher and Hoek show that throughout the year the female fish exceed the males in number, and, secondly, that during the earlier months of the year female fish run in much larger numbers than do male fish. It is only in September that anything like an equality between the two sexes is established. But in Great Britain it is not until the end of August that the nets are removed, and one cannot but believe that the destruction of such a very large proportion of females as are captured during the early months of the season must have a most prejudicial effect upon the breeding stock.
Rate of. Migration
By a comparison of the first appearance of winter salmon and of grilse in the markets of Holland and of Basel500 m. up the river - Miescher gives some data for the determination of the average rate at which salmon ascend an unobstructed stream. It was found that winter salmon appeared at Basel about 54 days after their appearance in Holland, which would give a rate of passage of about 10 m. per diem. From a smaller number of observations on grilse, it appears that they travel at a somewhat slower rate. It is, however, doubtful how far these figures are of value in deciding the rate at which fish pass up the lower reaches of the river.
Great difficulties have been experienced in ascertaining the age and rate of growth of salmon. The practice has long ago been resorted to of "marking" salmon, the most satisfactory mark being a small oblong silver label, oxidized or blackened, bearing distinctive letters and numbers, to the dorsal fin. But of late the structure of the scales has been studied with the object of obtaining indications of the age, growth and spawning habit. H. W. Johnston in 1905 contributed an interesting paper on the subject. The scales bear concentric lines, which vary in number and relative distance according to the growth of the fish, and during the feeding periods these lines are added with more rapidity and a greater degree of separation than at other times. Johnston has endeavoured to ascertain their meaning in Tay salmon, and he has shown that the number of lines external to their last annual ring gives some clue to the time at which they left the sea; he is thus able to distinguish among ascending salmon such as are on their first return from such as have made the journey once or oftener before.
The group of Pacific salmon, or king salmon, commonly designated as Oncorhynchus, contains the largest and commercially the most important of the Salmonidae. They are anadromous species inhabiting the North Pacific and entering the rivers of America as well as of Asia. The best known and most valuable is the quinnat (S. quinnat), ascending the large rivers in spring and summer, spawning from July to December. They die after the breeding season is over, and never return to the sea. For the important Salmonidae known as Trout, Char,Whitefish,Smelt,Grayling, &C., see the separate articles. The huchen (S. hucho) of the Danube is an elongate, somewhat pike-like form, growing to the same size 1 Winter fish not due to spawn till following November.
as the salmon, of silvery coloration, with numerous small black dots, extending on the dorsal fin. Allied to it are S. fluviatilis from Siberia and S. perryi or blackistoni from the northern island of Japan.
The genus Stenodus is intermediate between Salmo and Coregonus (whitefish). S. leucichthys is an anadromous species, inhabiting the Caspian Sea and ascending the Volga and the Ural; it is also found in the Arctic ocean, ascending the Ob, Lena, &c. It grows to a length of 5 ft. A second species occurs in Arctic North America; this is the "Inconnu," S. mackenzii, from the Mackenzie river and its tributaries.
The capelin (Mallotus villosus, so called from the villous bands formed by the scales of mature males) is a salmonid of the coasts of Arctic America and north-eastern Asia; it deposits its eggs in the sand along the shores in incredible numbers, the beach becoming a quivering mass of eggs and sand. Plecoglossus, a salmonid from Japan and Formosa, is highly remarkable for its lamellar, comb-like, lateral teeth. The siel-smelts, Argentina, are deep-sea salmonids, of which examples have occasionally been taken off the coasts of Scotland and Ireland. Bathylagus, another salmonid discovered by the "Challenger" expedition, is still better adapted for life at great depths (down to 1700 fathoms), the eyes being of enormous size.
Authorities
On the systematic and life histories: A. Gunther, Catalogue of Fishes in the British Museum, vol. vi. (1866); F. Day, British and Irish Salmonidae (London, 1887); F. A. Smitt, Kritisk FOrteckning ofver de i Riksmuseum befintliga Salmonider (Stockholm, 1886); V. Fatio, Faune des vertebras de la Suisse, vol. v. (1890); D. S. Jordan and B. W. Evermann, Fishes of North America, vol. i. (1896), and American Food and Game Fishes (London and New York, 1902); F. F. Kavraisky, Die Lachse der Kaukasuslc nder (Tiflis, 1896). On growth and migrations: Die histochemischen and physiologischen Arbeiten von Friedrich Miescher, Band ii., pp. 116, 192, 3 0 4, 325 (Leipzig, 1897); P. P. C. Hoek, Statische and biologische Untersuchungen an in den Niederldndern gefangenen Lachsen (Charlottenburg, 1895); Annual Reports of the Fishery Board for Scotland, part ii., "Report on Salmon Fisheries," Nos. 12, 13, 14 (18 9318 94-95-9 6); Report of Investigations on the Life-History of the Salmon to the Fishery Board for Scotland, edited by Noel Paton, presented to parliament and published 1898; K. Dahl, Orret og unglahs samt lovgivningens forhold til dem (Christiania, 1902); H. W. Johnston, "The Scales of Tay Salmon as indicative of Age, Growth and Spawning Habit," Ann. Rep. Fish. Board, Scotland, xxiii., appendix ii. (1905). Introduction in Tasmania and New Zealand: M. Allport, Proc. Zool. Soc. (1870), pp. 14 and 750; A. Nichol, Acclimatization of the Salmonidae at the Antipodes (London, 1882); W. Arthur, "History of Fish Culture in New Zealand," Tr. N. Zeal. Inst. xiv. (1881) p. 180; P. S. Seager, "Concise History of the Acclimatization of the Salmonids in Tasmania," Proc. R. Soc. Tasm. (1888) p. 1; also R. M. Johnston, l.c. p. 27. On the salmon disease: T. H. Huxley, Quart. Jour. Micr. Sci. xxii. (1882) p. 311. (G. A. B.)
